In a conventional RF discharge excitation laser apparatus, a voltage of, for example, several MHz to several hundreds of MHz, is applied across electrodes of a laser tube to generate a laser output. A matching circuit is arranged between an RF power source and the laser tube. The matching circuit matches an output impedance Z.sub.0 ' of the RF power source with an impedance (impedance of the laser tube) Z.sub.L ' between the electrodes of the laser tube, and an output voltage from the RF power source is effectively transmitted to the laser tube.
In the conventional RF discharge excitation laser apparatus described above, a discharge in a ceramic tube is produced by applying an RF voltage to the laser tube, which discharge excites the laser gas in the laser tube so that a laser beam is emitted.
Note, conventionally, a low-output type RF discharge excitation laser apparatus is used, and thus a ratio between the output impedance Z.sub.0 ' of the RF power source 101 the impedance Z.sub.L ' of the laser tube is relatively low (for example, Z.sub.O '/Z.sub.L '=2 to 5), and therefore, matching between the RF power source and the laser tube can be obtained by one matching circuit. More specifically, the conventional RF discharge excitation laser apparatus is provided with a laser tube having an inner diameter of the interior thereof of several millimeters, and when hundreds of volts are applied to the electrodes of such a laser tube, a laser output can be obtained An output voltage of the RF power source is, for example, 200 volts, and a match with the laser tube having an operating voltage of several hundreds of volts can be obtained by one matching circuit.
Recently, however, an RF discharge excitation laser apparatus has been developed which obtains a high-output laser beam upon an application of an RF voltage of several kilovolts to the laser tube. In an RF discharge excitation laser apparatus having such a high output, the inner diameter of the interior of the laser tube is several tens of millimeters (for example, 30 millimeters), and a voltage applied between the two electrodes of the laser tube is several kilovolts. For this reason, the ratio between the output impedance Z.sub.0 ' of the RF power source and impedance Z.sub.L ' of the laser tube is increased (for example, Z.sub.0 '/Z.sub.L ' &gt;10), and it is difficult to match the output impedance Z.sub.0 ' of the RF power source with the impedance Z.sub.L ' of the laser tube with only one matching circuit.